Benzoate/alkanoate ester compositions

ABSTRACT

Mixtures of esters produced by reacting an aromatic and an aliphatic monocarboxylic acid with a stoichiometric quantity of a diol are effective plasticizers for polyvinyl chloride and other rigid organic polymers. The freezing point of the mixtures and the efficacy of the present ester mixtures as plasticizers can be varied by adjusting the type and molar ratio of the two types of acids used to prepare the ester mixture.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to novel ester compositions. Moreparticularly, this invention relates to mixtures comprising 1) thediester of a diol containing from 2 to 6 carbon atoms and benzoic acidor a substituted benzoic acid, 2) a mixed ester of said diol, said acidand an aliphatic monocarboxylic acid and, 3) a diester of said diol andsaid aliphatic monocarboxylic acid. Small concentrations of themonoester of 1) said diol and 2) said aromatic and/or aliphaticcarboxylic acids can also be present.

[0003] Preferred ester compositions of this invention are low viscosityliquids at 25° C., are considerably less volatile and lower melting thanthe corresponding benzoic acid diesters, and are effective primaryplasticizers for rigid halogen-containing organic polymers such aspolyvinyl chloride.

[0004] 2. The Prior Art

[0005] Many esters of organic acids are known to be useful plasticizersfor a variety of organic polymers. Esters of 1) monohydric alcohols andphthalic acid and 2) mono- or dihydric alcohols and benzoic acid areparticularly preferred plasticizers for vinyl chloride homopolymers andcopolymers based on their cost and performance.

[0006] While esters of mono- or dihydric alcohols and aliphaticmonocarboxylic acids containing eight or more carbon atoms lower theviscosity and impart low temperature flexibility to vinyl chloridepolymers, the incompatibility of the aliphatic acid esters with thesepolymers limits their utility to secondary plasticizers in combinationwith benzoic or phthalic acid esters as the primary plasticizer. Adisadvantage of this approach is that the plasticizers selected may notbe compatible with one another and/or with the vinyl chloride or otherpolymer to which the ester mixture will be added as a plasticizer.

[0007] A second approach to combining the advantages of aliphatic andaromatic acids as plasticizers is to prepare a mixed ester. This can bedone by first forming a half ester by reacting a dihydric alcohol,hereinafter referred to as a diol, with half a molar equivalent of oneof the monocarboxylic acids or a suitable derivative thereof, such asthe corresponding acid halide. The resultant half ester is then isolatedand reacted with the other acid or a derivative thereof. The final estercan be represented by the generic formula R′C(O)ORO(O)CR″, where Rrepresents the hydrocarbon portion of a diol, R′ represents thehydrocarbon portion of the aromatic monocarboxylic acid and R″ thehydrocarbon portion of the aliphatic monocarboxylic acid.

[0008] The performance as plasticizers for polyvinyl chloride ofbenzoate/alkanoate mixed esters of the aliphatic diols ethylene glycol,diethylene glycol and 2-butene-1,4-diol is described by A. V. Bailey etal. in the Journal of the American Oil Chemists Society, 53 (5):176-8(1976). The esters were obtained by first reacting the desired diol withbenzoyl chloride and then reacting the resultant half ester with theacid chloride of desired aliphatic acid. These acids contained from 5 to20 carbon atoms.

[0009] Bailey et al. report that the benzoate/laurate mixed ester ofdiethylene glycol exhibits an optimum combination of properties as aplasticizer, one of the reasons being that the other plasticizersevaluated were incompatible with polyvinyl chloride at concentration of35 weight percent, based on the total weight of the polymer composition.

[0010] The mixed esters utilized by Bailey et al. are pure materialsthat require the two-stage preparation described in the precedingparagraphs using acid chlorides rather than the corresponding andrelatively less expensive carboxylic acids.

[0011] The present invention is based on the discovery that useful,relatively inexpensive mixtures of aromatic and aliphatic acid esterscan be prepared using a single step process. These ester compositionsare useful primary plasticizers for homo- and copolymers of vinylchloride and other rigid organic polymers.

[0012] In accordance with the present process a diol is reacted with astoichiometric amount of a mixture of 1) benzoic acid or other aromaticmonocarboxylic acid and 2) an aliphatic monocarboxylic acid. The molarratio of the two carboxylic acids is adjusted to achieve the desiredratio of the two acid residues in the reaction product. The molar ratioof total acids to diol is typically 2:1.

[0013] The present ester compositions are considerably easier and lessexpensive to prepare than the pure aromatic/aliphatic mixed esters ofthe prior art and exhibit unexpectedly low levels of viscosity andvolatility. Other advantages of the present ester compositions will bedescribed in the present specification.

DETAILED DESCRIPTION OF THE INVENTION

[0014] This invention provides ester compositions comprising

[0015] 1) an ester corresponding to formula (I)

R¹C(O)OR²O(O)CR³;  I

[0016] 2) an ester corresponding to formula (II)

R¹C(O)OR²O(O)CR¹;  II

and

[0017] 3) an ester corresponding to formula (III)

R³C(O)OR²O(O)CR³  III

[0018] wherein R′ is at least one radical selected from the groupconsisting of phenyl and alkyl-substituted phenyl, R² is a divalentradical of the formula —R⁴(OR⁴)m—, R³ is an alkyl radical containingfrom 3 to 21 carbon atoms, R⁴ is an alkyl radical containing from 2 to 4carbon atoms, and m represents 0 or the integer 1 or 2.

[0019] The present ester compositions are prepared by reacting a diol ofthe formula HOR²OH with an aromatic monocarboxylic acid of the formulaR¹C(O)OH and an aliphatic monocarboxylic acid of the formula R³C(O)OH,wherein the total moles of said aromatic and aliphatic carboxylic acidsare equal to twice the number of moles of said diol and R¹, R² and R³are as hereinbefore defined.

[0020] This invention also provides plasticized polymer compositionscomprising 1) a homopolymer or copolymer of vinyl chloride and 2) aplasticizer comprising a mixed ester composition of the presentinvention.

[0021] In preferred embodiments of the present ester compositions, themolar ratio of R¹C(O)— to R³ C(O)— groups in said composition is from3:1 to 12:1, R¹ is phenyl, m is 1 or 2, and the composition is a liquidat 25° C.

[0022] The ester compositions of this invention can optionally containup to about 5 percent by weight of monoesters of the diol HOR²OH and atleast one of the aromatic and aliphatic carboxylic acids used to preparethe ester. These monoesters are represented in this specification by theformulae R¹C(O)OR²OH and R³C(O)OR²OH, wherein R¹, R² and R³ are aspreviously defined. The presence of these monoesters is typically notdesirable because they increase the volatility of the ester composition.

[0023] To minimize the concentration of monoesters in the final estermixture, the moles of aromatic and aliphatic acids used to prepare theesters should be equal to twice the number of moles of diol. Theconcentration of monoesters can be further reduced by washing thismixture with an aqueous solution of a base such as potassium hydroxide.

[0024] An unexpected advantage of the present ester compositions is thatby selecting preferred ranges for the molar ratio of the twomonocarboxylic acids and the number of carbon atoms in the aliphaticcarboxylic acid, the physical properties such as melting point,viscosity and volatility exhibited by the resultant mixture of estersand the compatibility of these mixtures with vinyl chloride polymers canbe varied over a wide range to achieve a desired combination ofproperties. Preferred ester compositions and the molar ratio of aromaticto aliphatic carboxylic acids used to prepare them are described insubsequent sections of this specification.

[0025] Although the relative concentrations of the three possiblediesters in a composition of the present invention is difficult topredict, because carboxylic acids typically react at different rates,the distribution of reaction products is influenced by the relativeconcentrations of aromatic and aliphatic carboxylic acids in the initialreaction mixture, the temperature of the reaction mixture and the totalreaction time.

[0026] The accompanying examples demonstrate that a reaction mixturecontaining a 6:1 molar ratio of benzoic acid to the aliphatic carboxylicacid will produce an ester mixture containing a higher concentration ofmono- and dibenzoates and a lower concentration of the mixedbenzoate/alkanoate ester than a reaction mixture in which this molarratio is 1:1. The inability to precisely predict the relativeconcentrations of the possible mono- and diesters in the present estermixtures from the molar ratio of the two carboxylic acids used toprepare them does not affect the utility of the present mixtures asprimary plasticizers for polyvinyl chloride and other rigid organicpolymers.

[0027] Preparation of the Mixed Esters

[0028] The mixed ester compositions of this invention can be prepared byreacting the desired diol with a substantially equimolar quantity of amixture consisting essentially of 1) an aromatic carboxylic acidselected from the group consisting of benzoic acid and substitutedbenzoic acids and 2) an aliphatic monocarboxylic acid containing from 3to 21 carbon atoms. Substituted benzoic acids such as toluic acid can beused in place of benzoic acid. It will be understood by those skilled inthe art of ester preparation that derivatives of the aromatic andaliphatic carboxylic acids, such as the corresponding acyl halides andacid anhydrides, can be substituted for the acid.

[0029] While the molar ratio of the aromatic to the aliphatic carboxylicacid and the particular aromatic and aliphatic acids used to prepare theinitial reaction mixture are not critical with respect to operability ofthe process used to prepare the present compositions, the molar ratio ispreferably from 1 to 12 moles of the aromatic monocarboxylic acid permole of the aliphatic monocarboxylic acid, the aromatic carboxylic acidis preferably benzoic acid and the aliphatic carboxylic acid preferablycontains from 8 to 16 carbon atoms. These preferences are based on theproperties, particularly melting point and volatility, of the resultantester mixtures and the efficacy of the ester compositions asplasticizers for vinyl chloride polymers.

[0030] Diols suitable for use in preparing the ester compositions of thepresent invention can be represented by the general formulaHOR⁴(OR⁴)_(m)OH. In this formula R⁴ represents an alkyl radicalcontaining from 2 to 4 carbon atoms, and m represents 0 or the integer 1or 2.

[0031] Suitable diols include but are not limited to ethylene glycol,propylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, diethyleneglycol, dipropylene glycol, triethylene glycol, 1,3-butanediol and1,4-butanediol. Diols wherein R⁴ is ethyl or n-propyl and m is 1 or 2are preferred based on their cost and commercial availability.

[0032] Because esterification is typically a reversible reaction, thisreaction is typically conducted at the boiling point of the reactionmixture and the water produced as a by-product of the reaction ispreferably distilled from the reaction mixture and collected. Toincrease the rate of the esterification reaction, it is preferablyconducted in the presence of a suitable catalyst such as a mineral acid,an organotin compound, an organotitanium compound and/or a zirconiumcompound. Suitable catalysts include but are not limited to the organicsulfonic acids such as toluene sulfonic acid, tin compounds such asstannous octoate, tetrabutyl titanate and zirconium carbonate. Thesecatalysts can be used alone or in combinations of two or more.

[0033] The procedures and equipment used to prepare, isolate and analyzethe ester mixtures produced from the esterification reaction aresufficiently well known to those skilled in this art that a detaileddiscussion is not required as part of the present specification. Gaschromatography is a preferred method for determining the types andrelative concentration of the esters in the present compositions.

[0034] When equal numbers of moles of diethylene glycol, benzoic acidand lauric acid were reacted and the resultant mixture of esters treatedwith aqueous potassium hydroxide solution followed by washings withwater to reduce the concentration of monoesters, analysis of the productusing gas chromatography showed the mixture to contain less than 0.5percent diethylene glycol monobenzoate, 4 percent diethylene glycolmonolaurate, 14 percent diethylene glycol dibenzoate, 45 percentdiethylene glycol monobenzoate monolaurate and 36 percent diethyleneglycol dilaurate, based on the relative areas of the peaks on the outputchart of the chromatograph.

[0035] Properties of Preferred Mixed Esters

[0036] Ester mixtures prepared by reacting benzoic acid and a carboxylicacid containing from 9 to about 14 carbon atoms with one of the presentdiols are preferred based on their unexpected combination of propertiesthat make these esters particularly useful primary plasticizers fororganic polymers such as homopolymers and copolymers of vinyl chloride.

[0037] Data in the accompanying examples demonstrate that the viscosityand freezing point of these esters are unexpectedly low relative to thecorresponding diester of benzoic acid. As the molar ratio of benzoicacid to lauric acid in the initial reaction mixture increases from 1:1to 9:1 the freezing point of the resultant ester mixture decreases from25° C. to a eutectic point at about −15° C. As this ratio increasesbeyond 9:1 to the absence of the aliphatic carboxylic acid, the freezingpoint of the resultant ester mixture increases to about 25° C. fordiethylene glycol dibenzoate.

[0038] Performance of the Present Mixed Esters as Plasticizers

[0039] Mixed esters prepared from benzoic acid, an aliphatic carboxylicacid containing from 8 to 16 carbon atoms and a diol such as diethyleneglycol are particularly useful plasticizers based on the unique andunexpected combination of an unexpectedly low freezing point and lowvolatility of the mixed ester and the low viscosity and relatively lowgel temperature of the plasticized polymer. In addition to homo-andcopolymers of vinyl chloride, other types of polymers suitable for usewith the present ester compositions include but are not limited tothermoplastic polymers such as cellulose ester polymers, polystyrene,and chloronated polyethylene, and elastomers such as polyacrylics,styrene/butadiene copolymers and natural rubber.

[0040] The following examples describe preferred embodiments of thepresent ester mixtures, a preferred method for preparing them, thephysical properties of these mixtures and the properties of polyvinylchloride compositions containing these mixtures as primary plasticizers.The examples should not be interpreted as limiting the scope of theinvention defined in the accompanying claims. Unless otherwise specifiedall parts and percentages in the examples are by weight and the physicalproperties of the esters mixtures were measured at 25° C.

EXAMPLE 1

[0041] Four mixed ester compositions of the present invention wereprepared by charging a glass reactor with diethylene glycol(OHCH₂CH₂OCH₂CH₂OH) as the diol, benzoic acid as the aromatic carboxylicacid, lauric acid as the aliphatic carboxylic acid, and, as the catalystfor the esterification reaction, 0.1 percent, based on the weight oftotal reactants, of a catalyst mixture containing 75 weight percentzirconium carbonate and 25 weight percent stannous oxalate. The molarratio of benzoic to lauric acids present in the four initial reactionmixtures is listed in Table 1. The molar ratio of total carboxylic acidsto glycol was 2:1 in all of these reaction mixtures.

[0042] The reactor was equipped with a thermometer to measure thetemperature of the reaction mixture, a mechanically driven stirrer, aninlet for nitrogen extending below the surface of the reaction mixture,and a trap to collect the water that distilled as a by-product of theesterfication reaction. A water-cooled reflux condenser was locatedabove the trap.

[0043] The contents of the reactor were gradually heated to liquify thesolid reactants and initiate vaporization of volatile materials. At areaction mixture temperature of about 180° C. all of the initialreactants had liquified and vaporized liquid had begun to condense andcollect in the trap. The boiling point of the reaction mixture graduallyincreased to 250° C. Following about 4 hours of heating the acid numberof the reaction mixture was measured at 30 minute intervals until avalue of 5 or less was obtained. A small volume of diethylene glycol wasadded if the acid number was greater than 5 and did not change betweensuccessive samplings. When the acid number of the reaction mixturemeasured 5 or less, heating of the reaction mixture was discontinued andthe mixture allowed to cool to 90° C. At this time a volume of a 10weight percent aqueous potassium hydroxide solution equal to about ⅓ thevolume of the reaction mixture was added to the reactor. After about 15minutes of stirring the aqueous layer was separated and discarded. Theorganic layer was washed three times using volumes of 10 weight percentaqueous potassium hydroxide solution equal to that used for the firstwashing, followed by at least three washings with hot deionized wateruntil the pH of the organic layer was 7.

[0044] The types and relative concentrations of esters in the reactionproduct, a clear, colorless liquid, was determined using a HewlettPackard HP6890 series gas chromatograph equipped with a type HP-5 columnpacked with phenyldimethylpolysiloxane that was 5% crosslinked. Thecolumn temperature was gradually increased from 80 to 320° C. and therate of helium flow was 200 cc. per minute.

[0045] The chromatogram generated by passage of an ester mixture throughthe detector of the gas chromatograph contained four or five peaks, eachcorresponding to one of the component esters. The area under a givenpeak was considered directly proportional to the relative concentrationof the corresponding ester. Under the operating conditions of thechromatograph the esters emerged in the following order: themonobenzoate of diethylene glycol (DEGMB), the monolaurate (DEGML), thedibenzoate (DEGDB), the mixed benzoate/laurate (DEGBL) and the dilaurate(DEGDL).

[0046] The molar ratio of benzoic acid to lauric acid used for each ofthe four esterification reactions is recorded in Table 1, together withthe percent of total peak area on the chromatogram corresponding to eachof the aforementioned five possible products. In each of the initialreaction mixtures the molar ratio of diethylene glycol to totalcarboxylic acids was 1:2. TABLE 1 Benzoic Acid:Lauric Acid Mole Ratio¹ %DEGMB² % DEGML % DEGDB % DEGBL % DEGDL 1:1 (DEGBL) <0.5 4 14 45 36 3:1(DEG3BL) <0.5 <1 38 46 15 6:1 (DEG6BL) <0.5 <2 58 30 9 9:1 (DEG9BL) <0.5<1 72 22 4 12:1 (DEG12BL) <0.5 <1 77 19 2

EXAMPLE 2

[0047] This example demonstrates the relatively low freezing point,viscosity and volatility that make the present ester mixtures desirableplasticizers for polyvinyl chloride and other rigid organic polymers.

[0048] The freezing points of the esters mixtures described in Example 1that were liquid at ambient temperature were determined by exposing theester mixtures to a mixture of ethylene glycol and water that was cooledto the desired temperature using a refrigeration unit. The temperatureof the mixture containing a sample of the ester to be to be evaluatedwas initially 25° C. and was lowered in increments of 5° C. Eachtemperature level was maintained for 24 hours. The sample was examinedat the end of each 24-hour period to determine if the initially liquidester composition had solidified. The temperature at which solidmaterial was first observed was reported as the freezing point of theester mixture being evaluated and is recorded in Table 2. Forcomparative purposes, pure diethylene glycol dibenzoate freezes at 25°C.

[0049] The viscosities of the esters were measured at 25° C. using astress-controlled rheometer manufactured by TA Instruments and equippedwith a 4 cm-diameter cone-shaped plate.

[0050] The esters are identified in the same manner as in the precedingTable 1. TABLE 2 BENZOIC ACID/ LAURIC ACID MOLE RATIO FREEZING TEMP.(°C.) VISCOSITY @ 5° C.¹ 1:1 (DEGBL) 25 (Solid) 3:1 (DEG3BL) 5 0.13 6:1(DEG6BL) −5 0.15 9:1 (DEG9BL) −15 0.18 12:1 (DEG12BL) −10 0.28 DEGDB² 250.43 (supercooled)

[0051] The volatility of the esters was determined using a model TGA2950thermogravimetric analyzer manufactured by TA Instruments. Thepercentage weight change was measured by exposing the sample to atemperature of 190° C. for 3 hours under a flow of nitrogen at a rate of100 cc. per minute. The percent weight loss of each ester was determinedat 30 minute intervals and the results are recorded in Table 3.Di-2-ethylhexyl phthalate (DOP) was evaluated for comparative purposes.TABLE 3 % Weight Loss Time (Min.) DEGBL DEG3BL DEG6BL DEG9BL DEGDB DOP*0 0 0 0 0 0 0 30 9.8 11.4 14.5 11.2 28.7 18.1 60 20.6 23.3 28.0 23.153.0 37.1 90 29.8 32.6 37.2 33.5 71.0 56.1 120 37.8 41.1 47.1 42.9 83.476.0 150 44.7 48.7 58.0 51.0 92.1 90.4 180 50.7 55.4 64.5 60.0 100 95.7

[0052] The data in Tables 2 and 3 demonstrate the unexpectedly lowervolatility of DEG9BL relative to DEG6BL, which, in turn, exhibitedhigher values than DEG3BL. This is an unexpected reversal of theobserved trend toward higher values of viscosity and volatility withincreasing benzoic acid content.

EXAMPLE 3

[0053] This example demonstrates the utility of the mixed esters of thisinvention as plasticizers for polyvinyl chloride (PVC) compositions.Preferred esters of the present invention exhibit a unique combinationof high solvating ability for the polymer with a relatively lowviscosity of the plasticized polymer composition.

[0054] The ester compositions were incorporated into two plastisolformulations. The plasticizer was used at levels of 30 and 55 parts byweight per 100 parts of PVC resin(s).

[0055] The types and amounts of ingredients in the two formulationsevaluated are recorded in Table 4. TABLE 4 Formulation A B IngredientParts Parts PVC 100 60 Blending 0 40 Resin Plasticizer 55 30 TXIB¹ 3 6ESO² 4 4 Stabilizer³ 3 3

[0056] The polyvinyl chloride was prepared by microsuspensionpolymerization and exhibited a weight average molecular weight of200,000. It is available as Lacovyl PB 1302 from Atochem.

[0057] The blending resin was a vinyl chloride homopolymer prepared bysuspension polymerization, exhibited a weight average molecular weightof 140,000, and is available as Vinnolit C65V from Wacker Chemie. Thepurpose of the blending resin was to reduce the viscosity of theplastisol.

[0058] Both of these polymers were in the form of finely divided solids.

[0059] Plastisols were prepared by first blending the liquid ingredientsusing a high speed mixer. The resultant mixture was cooled using anice/water bath to prevent gelation of the composition during addition ofthe vinyl chloride polymer(s). Following addition of the polymer(s) thecomposition was stirred at a mixer speed of 1200 revolutions per minutefor 10 minutes then deaerated for 30 minutes under reduced pressure withstirring.

[0060] The viscosity of the resultant deaerated plastisols A and B weremeasured using a stress-controlled rheometer manufactured by TAInstruments. The spindle of the instrument was equipped with a platemeasuring 2 cm. in diameter. The shear rate was 10 sec.⁻¹ under ambientconditions.

[0061] The gelation temperatures of the plastisols were determined usingthe same rheometer and 2 cm.-diameter plate used to determine viscosity.In this instance the plate was oscillated rather than rotated as in thecase of the viscosity measurement. The temperature of the metal block onwhich the sample of plastisol rested was gradually increased untilgelation of the plasticizer occurred, which was evidenced by a suddenincrease in the torque required to oscillate the plate.

[0062] When changing the plasticizer in a plastisol results in alowering of the gelation temperature, this is associated with greatersolvating ability of the plasticizer. The viscosity and gelationtemperature of the plastisols evaluated are recorded in Table 4.

[0063] Plastisols corresponding to formulations A and B but usingdi2-ethylhexyl phthalate or a 1:1 weight ratio mixture of diethyleneglycol dibenzoate and triethylene glycol dibenzoate in place of a mixedester composition of the present invention were prepared and evaluatedfor comparative purposes.

[0064] The viscosity and gelation temperature of the plastisols arerecorded in Table 4. TABLE 4 Viscosity Gelation Temperature Plasticizer(Pa · s) (° C.) DEG3BL 1.1 67 DEG6BL 1.5 65 DEG9BL 1.6 65 DEGDB/ 3.5 63TEGDB¹ DOP 1.8 76

[0065] The data in Table 4 demonstrate the unique combination of lowviscosity and increased solvating ability, as evidenced by a lowergelation temperature, that distinguish preferred embodiments of thepresent mixed esters relative to widely used plasticizers for vinylchloride polymers.

EXAMPLE 4

[0066] This example demonstrates the compatibility of the present estermixtures with polyvinyl chloride.

[0067] The plastisols to be evaluated were coated on release paper andfused by heating at 200° C. for 2 minutes. The resultant sheets wereabout 1 mm. thick. Samples measuring 1×3 inches (2.54×7.62 cm.) were cutfrom the sheets. The samples were then removed from the paper backingand folded to form a U-shaped loop, compressed within a binder clip,heated and then evaluated in accordance with the procedure described inASTM test D 3291-92. The test samples were heated at 73° C. for 24hours. Following heating the curved interior portion of each sample wasdaubed with a cigarette paper to determine whether any plasticizer hadexuded from the polymer. The amount of exuded liquid was rated on ascale of from 0 (no liquid present), to 3 (surfaces of polymer and papercovered with continuous films of liquid exudate). All of the testsamples evaluated were rated “0” with the exception of the samplecontaining 55 parts by weight of the mixed ester referred to in Table 1as DEG3BL. This sample was given a rating of “1”, indicating only slightexudation with faint, discontinuous marks on the paper.

That which is claimed is:
 1. An ester composition comprising 1) an estercorresponding to formula (I) R¹C(O)OR²O(O)CR³  I 2) an estercorresponding to formula (II) R¹C(O)OR²O(O)CR¹;  II and 3)an estercorresponding to formula (III) R³C(O)OR²O(O)CR³  III wherein R¹ is atleast one radical selected from the group consisting of phenyl andalkyl-substituted phenyl, R² is a divalent radical of the formula—R⁴(OR⁴)_(m)—, R³ is an alkyl radical containing from 3 to 21 carbonatoms, R⁴ is an alkyl radical containing from 2 to 4 carbon atoms, and mrepresents 0 or the integer 1 or
 2. 2. A composition according to claim1 wherein the molar ratio of R¹C(O)— to R³C(O)— groups in saidcomposition is at least 1:1 and said composition is a liquid at 25° C.3. A composition according to claim 2 wherein said molar ratio is from1:1 to 12:1.
 4. A composition according to claim 3 wherein saidcomposition additionally contains at least one ester exhibiting aformula selected from the group consisting of R¹C(O)OR²OH andR³C(O)OR²OH.
 5. A composition according to claim 1 wherein R¹ is phenyl,m is 1 or 2 and R³ contains from 8 to 16 carbon atoms.
 6. A compositionaccording to claim 5 wherein R⁴ is ethyl or propyl and R³ contains 11carbon atoms.
 7. A plasticized polymer composition comprising 1) apolymer selected from the group consisting of homopolymers andcopolymers of vinyl chloride and 2) a plasticizer comprising 1) an estercorresponding to formula (1) R¹C(O)OR²O(O)CR³  I 2) an estercorresponding to formula (II) R¹C(O)OR²O(O)CR¹;  II and 3) an estercorresponding to formula (III) R³C(O)OR²O(O)CR³  III wherein R¹ is atleast one radical selected from the group consisting of phenyl andalkyl-substituted phenyl, R² is a divalent radical of the formula—R⁴(OR⁴)_(m)—, R³ is an alkyl radical containing from 3 to 21 carbonatoms, R⁴ is an alkyl radical containing from 2 to 4 carbon atoms, and mrepresents 0 or the integer 1 or
 2. 8. A polymer composition accordingto claim 7 wherein the molar ratio of R¹C(O)— to R³C(O)— groups in saidcomposition is at least 1:1, and said composition is a liquid at 25° C.9. A polymer composition according to claim 8 wherein said molar ratiois from 1:1 to 12:1.
 10. A polymer composition according to claim 7wherein R¹ is phenyl and m is 1 or 2 and R³. contains from 8 to 16carbon atoms.
 11. A polymer composition according to claim 10 wherein R⁴is ethyl or propyl and R3 contains 11 carbon atoms.